The Saturn AL-31 is a family of military turbofan engines. It was developed by Lyulka, now NPO Saturn, of Soviet Union, originally for the SukhoiSu-27 air superiority fighter. It produces a total thrust of 123 kN (27,600 lb) with afterburning in the AL-31F, 137 kN (30,800 lb) in the AL-31FM (AL-35F) and 145 kN (32,000 lb) in the AL-37FU variants. Currently it powers all Su-27 derivatives and the Chengdu J-10 multirole jet fighter which has been developed in China.

The AL-31FP and AL-37FU variants have thrust vectoring. The former is used in the Su-30MKI export version of the Su-30 for India & Sukhoi Su-30MKM for Malaysia . The AL-31FP can deflect its nozzle to a maximum of ±15° at a rate of 30°/sec. The vectoring nozzle is utilized primarily in the pitch plane. The AL-31FP is built in India by HAL at the Koraput facility under a deep technology transfer agreement.

It has a reputation for having a tremendous tolerance to severely disturbed air flow. In the twin-engined Su-27, the engines are interchangeable between left and right. The Mean Time Between Overhaul (MTBO) for the AL-31F is given at 1000 hours with a full-life span of 3000 hours. Some reports suggested that Russia was offering AL-31F to Iran to re-engine its F-14 Tomcat air fleet in the late 1990s.

According to Saturn`s Victor Mihailovic Chepkin, chief designer of the 117 and 117S engines, the Chinese WS-10 was developed with the aid of the AL-31`s maintenance technical documentation.[10] China can domestically produce most AL-31 parts for its own jet engine programs, but must import turbine blades from Russia.[11]

Intended to power the Su-35BM, the izdeliye 117S (AL-41F1S) is an upgrade of the AL-31F that uses technology from the AL-41F. The engine produces 142 kN (32,000 lb) of thrust in afterburner and 86.3 kN (19,400 lb) dry.[12] It features a fan 3% larger in diameter (932 millimetres (36.7 in) versus 905 millimetres (35.6 in)), advanced high- and low-pressure turbines, an all-new digital control system, and provisions for thrust-vectoring nozzles similar to the AL-31FP. This engine will have an assigned life of 4,000 hours and an MTBO of 1,000 hours.[13] The first flight of this engine was completed in an Su-35BM on 20 February 2008.[14] On 9 August 2010, Ufa-based company UMPO started supplying 117S engines (AL-41F1S) intended for Su-35S fighters.[15]

Related to the 117S is the izdeliye 117 (AL-41F1), a highly improved AL-31F derivative designed for the Sukhoi T-50 fighter. The engine features an increased diameter fan, new high and low pressure turbines, and a digital control system (FADEC). According to Sukhoi director Mikhail Pogosyan, the 117 is a new fifth generation engine built specifically for the PAK FA. Though the specifics of the 117 engine remain classified, the engine's thrust was increased by 24.5 kN (5,500 lbs) over the AL-31 while the engine weight was reduced by 150 kg (330 lb). The new engine produces 147 kN (33,067 lbf) of thrust in afterburner and has a dry weight of 1,420 kg (3,130 lb) and thrust-to-weight ratio of 10.5:1.[16] Like the AL-31F, the 117 has 4 low-pressure compressor (fan) and 9 high-pressure compressor stages.[17] Mikhail Pogosyan further mentioned that the 117 engine meets the Russian Air Force requirements and will be installed in production PAK-FA fighter which will be supplied to the Russian Air Force and prospective foreign clients.[18]

The 117 is an interim engine meant for prototype and initial production batches of the T-50. The definitive second stage for the aircraft is designated izdeliye 30 and will eventually replace the 117 after 2020. The new engine has increased thrust and fuel efficiency as well as improved reliability and lower costs. Bench testing of the new engine will start in 2014 according to the general designer-director of the NPO Saturn Eugeny Marchuk.[19]